Epigenetics - Blurring the Line Between Phenotype and Genotype

I caught a fascinating segment on Nova last night about a field of study called epigenetics. As I understand it, epigenetics is the study of how DNA is expressed in an individual. All of the DNA in your body is the same, but you have bone cells, hair cells, lung cells, etc. The differentiation between cell types is regulated by chemicals that attach to the DNA and turn on or off various portions of the DNA. This is how epigenetics work - specific chemicals turn on or off various portions of the DNA, allowing expression of the DNA to change.

But what's really fascinating is that they're finding through studies that what you do with your body (your phenotype) can actually affect the expression of genes in your offspring. This breaks a cardinal rule in Biology - that your phenotype does not affect your genotype. For example, if you cut off your arm, then have children, you aren't going to have one-armed children.

Strictly speaking, that rule stands, but functionally what the studies they were talking about in the program are showing is that genetically identical rats with different gene expression pass their flavor of gene expression on to their children. They also showed a cat clones with completely different fur pattern and color and eye color. Even the faces looked different, but they were genetically identical cats.

Is that fascinating or what? It's always just seemed intuitively obvious to me that the choices you make regarding your body could affect your offspring, but the biology textbooks have always told me I was wrong. As usual, the biology textbook writers did the best it could with incomplete data, but where they completely failed was by laying down as hard and fast law that your offspring were unaffected by your phenotype, rather than explaining that was the best understanding we had at the time.

I've noticed this trend increasing as I've grown up - scientists have become continuously more bold about proclaiming supposedly irrefutable facts. What is it about the priesthood of scientists that so often interferes with intellectual honesty? Why do they say "DNA is absolutely the only way you can pass anything on to your children." (The passage in my biology textbook was pretty close to that.) Instead, perhaps they should say "DNA is the only known method for passing information between generations, but theories abound and research continues to uncover new and exciting information."

The link at the top of the article to the Nova page has tons of good information including the complete video of the segment, slideshows, resources, etc.